1. Field of the Invention
The present invention relates to an asymmetric digital subscriber line system, and, more particularly, to a discrete multi-tone processor in an asymmetric digital subscriber line (ADSL) modem.
2. Description of the Related Art
Recently, as internet and data compression technologies progress, not only can simple text information be available over a network, but also audio and moving image can be transmitted in real time. Furthermore, for transmission of a significant amount of information, new communications media such as integrated services digital network (ISDN) or cable modems have been developed. ISDN allows for simultaneous use of data communications and telephone service, but reduces data communication speed by half. Cable modems are relatively costly for both installation and use.
In order to compensate for such drawbacks, the ADSL system has been proposed as the next generation technology. The ADSL system provides for high speed data communications using existing telephone lines. In other words, ADSL allows more data to be sent over an existing telephone line. ADSL supports data transfer rates up to 640 kilobytes per second (Kbps) when sending data and data rates up to 8 megabytes per second (Mbps) when receiving data from an exchange station. Since the exchange rate of data in data transmission and data reception is different, ADSL is referred to an asymmetric digital subscriber line.
A digital modem operable under the ADSL protocol, used for data transmission, is about 100 times faster than a conventional analog modem having data transfer rate of 56 Kbps. This means that a complicated internal algorithm is required in the ADSL system since there is a need to accurately receive and transmit a large quantity of data at high speed. Thus, the overall complexity of the system for realizing the complicated internal algorithm increases, as high-price and high-speed digital signal processors (DSP) are required by the ADSL system.
Furthermore, the balance of price and efficiency for an ADSL system becomes a challenging compromise. In order to reduce the price, the ADSL modem must have an optimum design in which hardware and software are appropriately divided. A conventional ADSL modem adopts a digital modulation/demodulation technique referred to as discrete multi-tone (DMT). The DMT modulation/demodulation method requires a large amount of repetitive computations, and the overall operation processing is conventionally performed by the DSP using software. Furthermore, a protocol signal for initializing an ADSL modem is produced by the DSP using software. Since performance of the DMT function and production of the protocol signal are performed in software, the conventional ADSL has the advantage of flexibility. However, in this case, a high-price and high-speed DSP operable at 100 million instructions per second (MIPS) or faster is required.
As a result, the conventional ADSL modem has a disadvantage in that the price of and the overall size of the modem are increased due to use of the high speed and high priced DSP. Furthermore, the conventional ADSL modem consumes more power.